Implantable medical devices (herein abbreviated IMD) are used by the medical industry for delivering various treatments to different kinds of medical conditions, whether they be heart conditions, gastrointestinal conditions or nervous system and brain conditions. Most IMDs require a source of power, either to operate the device, provide electrical stimulation to a part of the body as part of a treatment or therapy, or both. Since IMDs are implanted, various types of surgeries are required to insert the IMDs into a patient. These surgeries might be fully or minimally invasive however a surgery of sorts is required for placing the IMD inside the patient. Most state of the art IMDs employ a battery, which depending on the type of IMD and the kind of condition it is supposed to treat, may keep the IMD functioning for a number of years. For example, known intracardiac devices (herein abbreviated ICDs) such as the Evera™ and the Protecta™ ICD systems from Medtronic, the Ellipse™ ICD from St. Jude Medical and the INCEPTA™ ICD from Boston Scientific, have a battery which lasts on average 7 years, whereas known subcutaneous ICDs, such as the S-ICD™ from Cameron Health (now owned by Boston Scientific) require a battery replacement approximately every 5 years. In general, most IMDs are used to treat conditions which may accompany a patient for the duration of their life and as such, either the IMD or the power source must be replaced at some point in time. Whether the IMD is inserted via a fully invasive procedure or a minimally invasive procedure, when the batteries of the IMD are fully discharged, surgery is required to remove the IMD and replace it with a new one. As any kind of surgery involves potential health risks, there is a desire to increase the amount of time between battery replacements (and hence IMD replacements), thus reducing the number of surgeries a patient may go through while porting the IMD.
The design of state of the art IMDs has various constraints, one of them being size and weight. Whereas an increase in the size of the battery of an IMD may allow the IMD to function for a longer period of time, there is a constant motivation to reduce the physical size of IMDs such that they are less obtrusive to the patient and his body. One method for increasing the amount of time between battery replacements without increasing the size of the battery would be a more efficient battery which can store more charge per unit volume than current state of the art batteries. Another method is the use of rechargeable batteries which can be recharged wirelessly using energy transfer methods. Such batteries, also known as secondary cells, may not carry as much charge as a non-rechargeable battery, also known as a primary cell, however since they can be recharged, they may be able to power an IMD for a longer period of time before replacement is required. Even though secondary cells can only be recharged a finite number of times, the total amount of charge a rechargeable battery can give an IMD might be longer than the total charge stored on a primary cell, thereby increasing the time between battery replacements. For example, state of the art lithium-ion batteries can go through approximately 3000 charge-discharge cycles before requiring replacement, provided the batteries are completely discharged between cycles.
IMDs utilizing rechargeable batteries are known in the art. US Patent Application Publication No. 2008/0312725 A1, to Penner, assigned to E-Pacing, Inc., entitled “Implantable devices and methods for stimulation of cardiac and other tissues” is directed to an implantable system for stimulation of the heart, phrenic nerve or other tissue structures accessible via a patient's airway. The stimulation system includes an implantable controller housing which includes a pulse generator, an electrical lead attachable to the pulse generator and an electrode carried by the electrical lead. The electrode is positionable and fixable at a selected position within an airway of a patient. The controller housing may be adaptable for implantation subcutaneously, or alternatively, at a selected position within the patient's trachea or bronchus. The controller housing is proportioned to substantially permit airflow through the patient's airway around the housing. The pulse generator may be operable to deliver one or more electrical pulses effective in cardiac pacing, cardiac defibrillation, cardioversion, cardiac resynchronization therapy, or a combination thereof and includes a power source. In one embodiment, the system may further include a cannula adaptable for passage of the electrical lead through a wall of the trachea or bronchus. In another embodiment, the system may further include a tissue interface for wirelessly communicating an electrical signal through a wall of the trachea or bronchus. The power source may be a rechargeable power source, charged using electromagnetic charging. Other wireless charging methods may be used, for example, magnetic induction, radio frequency charging or light energy charging. The power source may also be charged by direct charging, such as via a catheter, through an endotracheal tube or during bronchoscopy, for example, to a charging receptacle, feedthrough or other interface optionally included in the pulse generator.
US Patent Application Publication No. 2010/0076524 A1, to Forsberg et al., assigned to Medtronic, Inc., entitled “Inductively rechargeable external energy source, charger, system and method for a transcutaneous inductive charger for an implantable medical device” is directed to a system that comprises an implantable medical device operationally coupled to receive energy from a secondary coil. An antenna is adapted to be positioned at a selected location relative to the secondary coil. An external power source is coupled to generate a signal in the antenna at any selected frequency that is within a predetermined frequency range to transcutaneously transfer energy from the antenna to the secondary coil when the implantable medical device is implanted in a patient. A core is selectably positionable relative to the antenna to focus the energy while the antenna is in the selected location. This application is also directed to an improved mechanism for transcutaneously transferring energy from an external power source to an implantable medical device. The method comprises positioning an antenna in proximity of the implantable medical device, laterally adjusting a position of a core of the antenna relative to the implantable medical device while the antenna is maintained substantially stationary, and adjusting a frequency of transmission of a power source. The method may further comprise driving the antenna with the power source at the adjusted frequency to transfer energy transcutaneously to the implantable medical device.
US Patent Application Publication No. 2011/0004278 A1, to Aghassian et al., assigned to Boston Scientific Neuromodulation Corporation, entitled “External charger for a medical implantable device using field sensing coils to improve coupling” is directed to a method for assessing the alignment between an external charger and an implantable medical device. By incorporating magnetic field sensing coils in an external charger, it is possible to determine the position of an implantable device by sensing the reflected magnetic field from the implant. In one embodiment, two or more field sensing coils are arranged to sense the reflected magnetic field. By comparing the relative reflected magnetic field strengths of the sensing coils, the position of the implant relative to the external charger can be determined. Audio and/or visual feedback can then be communicated to a patient to allow the patient to improve the alignment of the charger.
US Patent Application Publication No. 2012/0032522 A1, to Schatz et al., entitled “Wireless energy transfer for implantable devices” is directed to improved configurations for a wireless power transfer, employing repeater resonators to improve the power transfer characteristics between source and device resonators. A wireless energy transfer system for powering devices implanted in a patient is described. The system comprises a high-Q source resonator having a first resonant frequency, the source resonator being external to the patient, coupled to a power source and configured to generate oscillating magnetic fields at substantially a first resonant frequency. The system also comprises a high-Q device resonator having a second resonant frequency, the device resonator coupled to an implantable device requiring a supply power, the device resonator being internal to the patient and configured to capture the oscillating magnetic fields generated by the source resonator. The system further comprises a repeater resonator, wherein the repeater resonator is positioned to improve the energy transfer between the source resonator and the device resonator.